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  <title>从关联数组中取得键名</title>
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  <div id="layout-content"><div id="function.key" class="refentry">
   <div class="refnamediv">
    <h1 class="refname">key</h1>
    <p class="verinfo">(PHP 4, PHP 5, PHP 7, PHP 8)</p><p class="refpurpose"><span class="refname">key</span> &mdash; <span class="dc-title">从关联数组中取得键名</span></p>

   </div>
 <div class="refsect1 description" id="refsect1-function.key-description">
  <h3 class="title">说明</h3>
  <div class="methodsynopsis dc-description">
   <span class="methodname"><strong>key</strong></span>(<span class="methodparam"><span class="type"><span class="type">array</span>|<span class="type">object</span></span> <code class="parameter">$array</code></span>): <span class="type"><span class="type">int</span>|<span class="type">string</span>|<span class="type">null</span></span></div>

    <p class="para rdfs-comment">
     <span class="function"><strong>key()</strong></span> 返回数组中当前单元的键名。
    </p>
   </div>

  <div class="refsect1 parameters" id="refsect1-function.key-parameters">
  <h3 class="title">参数</h3>
  <p class="para">
   <dl>
    
     <dt>
<code class="parameter">array</code></dt>

     <dd>

      <p class="para">
       该数组。
      </p>
     </dd>

    
   </dl>

  </p>
 </div>

 <div class="refsect1 returnvalues" id="refsect1-function.key-returnvalues">
  <h3 class="title">返回值</h3>
  <p class="para">
   <span class="function"><strong>key()</strong></span> 函数返回数组中内部指针指向的当前单元的键名。
   但它不会移动指针。如果内部指针超过了元素列表尾部，或者数组是空的，<span class="function"><strong>key()</strong></span> 会返回 <strong><code>null</code></strong>。
  </p>
 </div>


 <div class="refsect1 changelog" id="refsect1-function.key-changelog">
  <h3 class="title">更新日志</h3>
  <table class="doctable informaltable">
   
    <thead>
     <tr>
      <th>版本</th>
      <th>说明</th>
     </tr>

    </thead>

    <tbody class="tbody">
     <tr>
 <td>8.1.0</td>
 <td>
  弃用在 <span class="type">object</span> 上调用此函数。
  在 <span class="type">object</span> 优先使用 <span class="function"><a href="function.get-mangled-object-vars.html" class="function">get_mangled_object_vars()</a></span> 或者使用 <span class="classname"><a href="class.arrayiterator.html" class="classname">ArrayIterator</a></span>。
 </td>
</tr>


    </tbody>
   
  </table>

 </div>


 <div class="refsect1 examples" id="refsect1-function.key-examples">
  <h3 class="title">范例</h3>
  <p class="para">
   <div class="example" id="example-4992">
    <p><strong>示例 #1 <span class="function"><strong>key()</strong></span> 例子</strong></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$array&nbsp;</span><span style="color: #007700">=&nbsp;array(<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'fruit1'&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #DD0000">'apple'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'fruit2'&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #DD0000">'orange'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'fruit3'&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #DD0000">'grape'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'fruit4'&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #DD0000">'apple'</span><span style="color: #007700">,<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #DD0000">'fruit5'&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #DD0000">'apple'</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">//&nbsp;此循环将会输出数组中所有值等于&nbsp;“apple”&nbsp;的键（key）<br /></span><span style="color: #007700">while&nbsp;(</span><span style="color: #0000BB">$fruit_name&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">current</span><span style="color: #007700">(</span><span style="color: #0000BB">$array</span><span style="color: #007700">))&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(</span><span style="color: #0000BB">$fruit_name&nbsp;</span><span style="color: #007700">==&nbsp;</span><span style="color: #DD0000">'apple'</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #0000BB">key</span><span style="color: #007700">(</span><span style="color: #0000BB">$array</span><span style="color: #007700">),&nbsp;</span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">next</span><span style="color: #007700">(</span><span style="color: #0000BB">$array</span><span style="color: #007700">);<br />}<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

    <div class="example-contents"><p>以上例程会输出：</p></div>
    <div class="example-contents screen">
<div class="cdata"><pre>
fruit1
fruit4
fruit5
</pre></div>
    </div>
   </div>
  </p>
 </div>

 <div class="refsect1 seealso" id="refsect1-function.key-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><span class="function"><a href="function.current.html" class="function" rel="rdfs-seeAlso">current()</a> - 返回数组中的当前值</span></li>
    <li class="member"><span class="function"><a href="function.next.html" class="function" rel="rdfs-seeAlso">next()</a> - 将数组中的内部指针向前移动一位</span></li>
    <li class="member"><span class="function"><a href="function.array-key-first.html" class="function" rel="rdfs-seeAlso">array_key_first()</a> - 获取指定数组的第一个键</span></li>
    <li class="member"><a href="control-structures.foreach.html" class="link">foreach</a></li>
   </ul>
  </p>
 </div>

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